1. Field of Invention
This invention relates to swimming aids, specifically to such devices which attach to the feet of a swimmer and create propulsion from a kicking motion as well as to propulsion foils used to generate propulsion.
2. Description of Prior Art
Prior art swim fin blades using flexible blades that flex to form a scoop shape during use are vulnerable to longitudinal compression forces if the entire blade system bends around a transverse axis to a reduced angle of attack. When the blade bends around a transverse axis to a reduced angle of attack, the central portion of the longitudinal scoop is forced to flex around a bending radius that is smaller than the bending radius occurring at the outer edges of the longitudinal scoop. The transverse bending of the outer scoop edges forces the central portions of the longitudinal scoop to contract in a longitudinal manner toward the foot pocket. Because prior art blade designs do not recognize this problem or provide any suitable solutions, the blade's resistance to contraction prevents the blade from forming the scoop shape during use and the scoop advantage is lost. Longitudinal compression forces created by the deflection of the blade around a transverse axis cause the scoop shape to collapse. As the degree of deflection increases around a transverse axis, the blade's resistance to forming a scoop is also increased. As a result, only a small portion of the blade's surface area near the tip of the fin is able to form a scoop and the back pressure within the blade also causes the depth of the collapsed scoop to be very small or often negligible.